An electrophotographic printing system needs to continually regulate the toning/image density of the imaging subsystem by periodically reading image density and adjusting various imaging parameters to maintain the desired image density. The image density can be read and adjusted by printing a uniformly toned density patch onto a media transport mechanism and reading the density of the printed patch with a densitometer, such as for example an on-line densitometer described in copending U.S. patent application Ser. No. 60/420,514, filed Oct. 23, 2002, in the names of Runkowske, et al. In order to maintain accurate control of the image density, a density patch must be periodically imaged on the media transport mechanism and read by the on-line densitometers followed by the appropriate print control adjustments to maintain an accurate/consistent density level.
U.S. Pat. No. 5,541,708, issued Jul. 30, 1996, shows one method for laying down and reading density patches for controlling print density in an electrophotographic reproduction apparatus. With this arrangement and method, the image density patches are formed on a moving endless belt, during subsequent rotations of the endless belt, so as to be at different locations relative to the belt from a position where the density patches were previously formed in each rotation cycle of the endless belt means. The purported advantages of this arrangement and method was to prevent density readings which are adversely effected by residual response effects on the endless belt, or premature aging effects at the cite of a density patch.